1. Field of the Invention
The present invention relates to a magnetic levitation rotating machine which performs levitation support control of a rotator, provided with a magnetic material as an object to be controlled, so that the rotator is supported in a levitated state at a desired position in a noncontact manner through the utilization of magnetic attraction force or magnetic repulsion force generated by an electromagnet or a permanent magnet. More particularly, the present invention relates to a detection mechanism for detecting the axial displacement and the rotating speed of the rotator.
2. Description of the Related Art
FIG. 10 is a diagram showing a general example of the construction of a conventional magnetic bearing mechanism, and FIG. 11 is a diagram showing an example of the construction of a control unit for performing levitation support control of the magnetic bearing. In the magnetic levitation rotating machine, a rotator R is driven and rotated by a motor in a noncontact manner, and, in addition, is supported in a levitated state by a radial magnetic bearing and a thrust magnetic bearing. The rotator R is provided with a target member 21 of a magnetic material, and is supported in a levitated state at a radial target levitation position by controlling magnetic attraction force generated from a radial support electromagnet 20. A radial displacement sensor 11 is provided near the electromagnet 20. The radial displacement sensor 11 measures the radial displacement (location) of a target magnetic material 19 provided in the rotator R. Further, the rotator R is provided with a thrust disk 18 formed of a magnetic material, and an axial levitation support electromagnet 15 for the rotator R is disposed so as to sandwich the thrust disk 18 thereby. The rotator R provided with the thrust disk 18 is supported in the levitated state at an axial target levitation position by controlling magnetic attraction force generated from the axial levitation support electromagnet 15.
A target 16, formed of a magnetic material, for a position sensor is provided at the shaft end of the rotator R, and an axial displacement sensor 13 for the rotator R is provided on the fixed side to measure the axial displacement of the rotator R. The rotator R is provided with a rotating speed detection disk 17, and a rotating speed detection sensor 14 is provided on the fixed side in its position near the rotating speed detection disk 17. Here all the displacement sensors 11, 12, 13 are sensors utilizing such a phenomenon that magnetic characteristics are changed in response to the displacement of a target (magnetic) material, such as an eddy current sensor or an inductance sensor. The rotating speed detection disk 17 has a concave or a convex, and passage through the concave or the convex is detected by a displacement sensor utilizing the same magnetic properties as described above to detect the rotating speed. In the example of the construction of the conventional magnetic bearing mechanism shown in FIG. 10, two sensors 11, 12 for detecting the radial displacement are shown. In fact, however, two additional sensors are disposed in a direction perpendicular to the paper surface. The sensors can detect a coordinate position within a plane perpendicular to the rotating shaft of the rotator.
In the prior art, as shown in FIG. 11, the axial displacement sensor 13, the rotating speed detection sensor 14, and the axial levitation support electromagnet 15 are disposed in a hierarchical structure manner on the fixed side of the magnetic bearing mechanism along the axial direction of the rotator R. As shown in FIG. 11, a signal, on the axial position (displacement) of the rotator R, obtained by the axial displacement sensor 13 is sent through a sensor signal processor 23 and a compensation circuit 24 provided within the control unit to an exciting current output amplifier 25 that outputs exciting current which is then supplied to the axial levitation support electromagnet 15 to perform excitation, whereby the rotator R is controlled so as to be levitated and supported at an axial predetermined position. Likewise, the output of the rotating speed detection sensor 14 is input into a rotation sensor signal processor 26, provided within the control unit, where the rotating speed is computed. The rotating speed value thus obtained is compared with a target rotating speed in a rotating speed controlling unit 27, and a current for driving the motor is supplied from an inverter 28 to the motor (not shown in FIG. 10) so that the rotating speed is brought to a predetermined value.
A great feature of the magnetic levitation rotating machine, wherein a rotator is supported in a levitated state by the above-described series of magnetic levitation controls, is such that the rotator, even when located at any position, is supported in a levitated state and rotated in a noncontact manner. Therefore, a noncontact rotating speed detection system should also be used in rotating speed detection means at the time of the application of rotating force by an induction machine or a synchronous machine.
Specifically, in addition to a displacement sensor element for levitation position detection for performing levitation support control of the rotator, a rotating speed detection sensor element should be installed. In the conventional techniques, however, as with the displacement sensor for position detection for magnetic levitation control, rotating speed detection sensors of an eddy current type, induction type, or inductance type, which is an electromagnetic detection method, have been generally used. When the electromagnetic sensor of the conventional type is used, however, for some mechanical arrangement of the sensors, a mutual electromagnetic interference phenomenon occurs. Therefore, the rotating speed detection sensor element and the displacement sensor element for position detection should be provided while leaving a space therebetween.
That is, in order to operate the above structure without any electromagnetic trouble, in FIG. 10, a certain space should be provided between the axial displacement sensor 13 and the rotating speed detection sensor 14 and between the rotating speed detection sensor 14 and the axial levitation support electromagnet 15. Therefore, there is a limitation on a reduction in size of the shaft end portion in the magnetic bearing mechanism.
Further, in the conventional system, as shown in FIG. 10, in the detection of the rotating speed, a method has been used wherein a rotating speed detection disk 17 partially provided with a notch is provided at the shaft end of the rotator and the disk is rotated together with the rotator and, in this case, when the notch has passed the front of the rotating speed detection sensor, a pulse signal synchronized with the rotating speed is generated. In this method, however, leaked magnetic flux of the magnetic levitation electromagnet is introduced into a portion around the rotating speed detection disk 17, and this deteriorates the S/N ratio of the rotating speed detection sensor signal. For this reason, the disposition of the rotating speed detection disk 17, the axial displacement sensor target 16, and the thrust disk 18 while leaving a certain space among one another is unavoidably necessary from the viewpoint of structure.
As described above, due to the above-described restrictions, the noncontact-type rotating speed detection sensor, based on an electromagnetic principle, which is provided within the magnetic bearing mechanism for levitating and supporting the rotator, should be provided while leaving a certain space, for example, from the electromagnet and the displacement sensor for position detection constituting the magnetic bearing mechanism. This is an obstacle to a reduction in size of the whole magnetic bearing mechanism.
In the rotating speed detection system of the rotating speed detection sensor, the adoption of a system utilizing an optical or other semiconductor sensor, which is not electromagnetic means, is considered effective for avoiding some of the above restrictions. Semiconductor sensors, however, are not suitable for applications of magnetic levitation rotating machines because they have problems including that semiconductor sensors are expensive and thus increase the cost, have low heat resistance, and suffer from complicate incorporated structure.
The present invention has been made under the above circumstances, and it is an object of the present invention to provide a magnetic levitation rotating machine which can realize stable displacement detection and rotating speed detection of the rotator and, in addition, can reduce the size of the whole system, that is, can render the whole system compact.
According to one aspect of the present invention, there is provided a magnetic levitation rotating machine for supporting a rotator in a levitated state by magnetic force of an electromagnet or a permanent magnet, the magnetic levitation rotating machine comprising: a position detection plane provided in the rotator and a concave and/or a convex provided in the plane; a displacement sensor provided on the fixed side, for detecting the position displacement of the plane including the concave or the convex; and a detection mechanism for detecting the displacement of the rotator and the rotating speed of the rotator from the output of the displacement sensor.
According to this construction, the detection of the displacement of the rotator and the detection of the rotating speed can be carried out using a single target member. Therefore, the structure of the magnetic bearing is simplified, and the size of this site can be reduced. In addition, the number of necessary components is reduced, leading to a reduction in cost.
Preferably, the displacement of the rotator is detected by extracting, from the output of the displacement sensor, the output of the displacement of the plane with the component representing the concave or the convex being removed therefrom.
Preferably, the rotating speed of the rotator is detected by extracting, from the output of the displacement sensor, pulse output corresponding to the concave or the convex.
In the magnetic levitation rotating machine, preferably, at least one pair of the displacement sensors is disposed at an arbitrary angle to the center of rotation of the rotator, the detection plane is disposed so as to face the displacement sensors, the concave and the convex are disposed so as to correspond to the positions of the displacement sensors at the same angle as the arbitrary angle, at which the displacement sensors are disposed, to the center of rotation of the plane, and the position displacement and rotating speed of the detection plane are computed from the outputs of the at least one pair of the displacement sensors and are output to enable the detection of both the displacement of the rotator and the rotating speed of the rotator.
The provision of the concave and the convex in the detection plane permits the axial displacement and the rotating speed of the rotator to be detected separately from each other without mutual interference.
Preferably, the detection plane is disposed in a thrust disk of a magnetic material which is an object to be controlled by an electromagnet for axial position control. This construction can eliminate the need to provide a disk fixed to the rotator for detecting the rotating speed and thus can shorten the length of the whole machine and can reduce the size of the whole machine.
In summary, according to the present invention, the rotating speed detection sensor, which has hitherto been an obstacle to a reduction in size, can be simplified. Therefore, the size of the magnetic bearing mechanism can be reduced and the cost can be reduced by virtue of the reduced number of components necessary for constituting the magnetic bearing mechanism.
The above and other objects, features, and advantages of the present invention will be apparent from the following description when taken in conjunction with the accompanying drawings which illustrates preferred embodiments of the present invention by way of example.